/*
 * Copyright 2002-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.resource;

import java.util.List;

import reactor.core.publisher.Mono;

import org.springframework.cache.Cache;
import org.springframework.cache.CacheManager;
import org.springframework.core.io.Resource;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.web.server.ServerWebExchange;

/**
 * A {@link ResourceResolver} that resolves resources from a {@link Cache} or
 * otherwise delegates to the resolver chain and caches the result.
 *
 * @author Rossen Stoyanchev
 * @author Brian Clozel
 * @since 5.0
 */
public class CachingResourceResolver extends AbstractResourceResolver {

    public static final String RESOLVED_RESOURCE_CACHE_KEY_PREFIX = "resolvedResource:";

    public static final String RESOLVED_URL_PATH_CACHE_KEY_PREFIX = "resolvedUrlPath:";


    private final Cache cache;


    public CachingResourceResolver(Cache cache) {
        Assert.notNull(cache, "Cache is required");
        this.cache = cache;
    }

    public CachingResourceResolver(CacheManager cacheManager, String cacheName) {
        Cache cache = cacheManager.getCache(cacheName);
        if (cache == null) {
            throw new IllegalArgumentException("Cache '" + cacheName + "' not found");
        }
        this.cache = cache;
    }


    /**
     * Return the configured {@code Cache}.
     */
    public Cache getCache() {
        return this.cache;
    }


    @Override
    protected Mono<Resource> resolveResourceInternal(@Nullable ServerWebExchange exchange,
            String requestPath, List<? extends Resource> locations, ResourceResolverChain chain) {

        String key = computeKey(exchange, requestPath);
        Resource cachedResource = this.cache.get(key, Resource.class);

        if (cachedResource != null) {
            if (logger.isTraceEnabled()) {
                logger.trace("Found match: " + cachedResource);
            }
            return Mono.just(cachedResource);
        }

        return chain.resolveResource(exchange, requestPath, locations)
                .doOnNext(resource -> {
                    if (logger.isTraceEnabled()) {
                        logger.trace("Putting resolved resource in cache: " + resource);
                    }
                    this.cache.put(key, resource);
                });
    }

    protected String computeKey(@Nullable ServerWebExchange exchange, String requestPath) {
        StringBuilder key = new StringBuilder(RESOLVED_RESOURCE_CACHE_KEY_PREFIX);
        key.append(requestPath);
        if (exchange != null) {
            String encoding = exchange.getRequest().getHeaders().getFirst("Accept-Encoding");
            if (encoding != null && encoding.contains("gzip")) {
                key.append("+encoding=gzip");
            }
        }
        return key.toString();
    }

    @Override
    protected Mono<String> resolveUrlPathInternal(String resourceUrlPath,
            List<? extends Resource> locations, ResourceResolverChain chain) {

        String key = RESOLVED_URL_PATH_CACHE_KEY_PREFIX + resourceUrlPath;
        String cachedUrlPath = this.cache.get(key, String.class);

        if (cachedUrlPath != null) {
            if (logger.isTraceEnabled()) {
                logger.trace("Found match: \"" + cachedUrlPath + "\"");
            }
            return Mono.just(cachedUrlPath);
        }

        return chain.resolveUrlPath(resourceUrlPath, locations)
                .doOnNext(resolvedPath -> {
                    if (logger.isTraceEnabled()) {
                        logger.trace("Putting resolved resource URL path in cache: \"" + resolvedPath + "\"");
                    }
                    this.cache.put(key, resolvedPath);
                });
    }

}
